Conformational study of internally retrograde and quasi-retrograde molecules — An ab initio and DFT study

2005 ◽  
Vol 83 (2) ◽  
pp. 122-137 ◽  
Author(s):  
Miguel A Zamora ◽  
Luis N Santágata ◽  
Marcelo F Masman ◽  
José A Bombasaro ◽  
Mónica L Freile ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Basis Sets ◽  
Conformational Study ◽  
Functional Theory ◽  
Large Size ◽  
Conformational Preferences ◽  
Comprehensive Picture ◽  
Homologue Series ◽  
Ab Initio And Dft

A conformational study of the symmetrical and nonsymmetrical homologue series was carried out. In this study, ab initio (RHF/3-21G and RHF/6-31G(d)) and density functional theory (B3LYP/6-31G(d)) calculations were performed. The presence of two symmetrical aromatic systems (identical or not) reduces notably the conformational possibilities of these compounds. Our results indicate that RHF/3-21G calculations are sufficient to use in a preliminary form. However, from our results it is prudent to use this technique only for a preliminary or exploratory conformational analysis. Thus, at least, the HF level of theory in conjunction with more extended basis sets and the inclusion of electron correlation appear to be necessary to confirm critical points at the potential energy hyper surfaces (PEHSs) and to assign the conformational preferences of these compounds. In the present paper, we report a complete and comprehensive picture of the conformational intricacies of the compounds with a small flexible connecting chain (n = 1–5). In addition, an "educated guess" for the conformational behaviour of large-size homologues (n = 6–10) is also reported.Key words: ab initio and DFT calculations, conformational study, homologue series.

scholarly journals NMR and Theoretical Studies on the Conformational Preferences of Some Non-metal Coordinated N-Enoyl Systems Attached to Common Chiral Auxilaries

2017 ◽  
Vol 58 (2) ◽  
Author(s):  
Rosmarbel Morales-Nava ◽  
Alejandro Ramírez-Solís ◽  
Mario Fernández-Zertuche
Keyword(s):  
Density Functional ◽  
Vibrational Analysis ◽  
Basis Sets ◽  
Chiral Auxiliaries ◽  
Nmr Studies ◽  
Stable Conformation ◽  
Functional Theory ◽  
Exchange Correlation ◽  
H Nmr ◽  
Conformational Preferences

<p>We report a systematic study of a series of N-enoyl systems attached to common oxazolidin-2-ones, oxazolidine-2-thiones and thiazolidine-2-thiones chiral auxiliaries in order to determine the most stable conformation of these compounds. <sup>1</sup>H NMR studies show an <em>anti</em>-<em>s</em>-<em>cis</em> structure as the most stable conformation for these series of compounds. Density Functional Theory geometry optimizations and vibrational analysis using the b3lyp exchange-correlation functional with the standard 6-31g** basis sets were done, including solvent effects (chloroform and toluene). Gibbs free energy differences show that the <em>anti</em>-<em>s</em>-<em>cis</em> structures are the most stable conformers lying, on average, ca. 6 kcal/mol lower in energy than the <em>syn</em>-<em>s</em>-<em>cis</em> conformers, widely used to explain the structure and reactivity of <em>N</em>-enoyl systems.</p>

scholarly journals Динамические поляризуемости двухатомных молекул: сравнение методов ab initio и теории функционала плотности с методом замещенной функции Грина теории квантового дефекта

2019 ◽  
Vol 127 (11) ◽  
pp. 736
Author(s):  
А.С. Корнев ◽  
К.И. Суворов ◽  
В.Е. Чернов ◽  
И.В. Копытин ◽  
Б.А. Зон
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Density Functional ◽  
Ab Initio Methods ◽  
Test Results ◽  
Dft Methods ◽  
Functional Theory ◽  
Frequency Dependent ◽  
Quantum Defect Theory ◽  
Ab Initio And Dft

The quantum defect theory is used to test the accuracy of ab initio methods and density functional theory (DFT) in calculating the frequency-dependent polarizabilities of diatomic molecules. We confine ourselves to testing only those variants of these methods that are most accurate for calculating static polarizabilities. The test results show that one of the main errors of the ab initio and DFT methods is associated with inaccuracies in determining the energies of excited states, where frequency-dependent polarizabilities have resonance maxima.

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

AB INITIO AND DFT STUDY OF NON-COVALENT INTERACTIONS BETWEEN RARE GAS ATOMS AND AROMATIC RINGS

2013 ◽  
Vol 12 (03) ◽  
pp. 1350012 ◽  
Author(s):  
CHENG CHENG ◽  
MIN ZHANG ◽  
LI SHENG
Keyword(s):  
Ab Initio ◽  
Weak Interaction ◽  
Density Functional ◽  
Nbo Analysis ◽  
Basis Sets ◽  
Rare Gas ◽  
Aromatic Rings ◽  
Functional Theory ◽  
Rare Gas Atoms ◽  
Non Covalent Interactions

In this paper, the weak interaction between aromatic rings (ARs) and rare gas (Rg) atoms has been studied using ab initio calculation and density functional theory (DFT). The augmented Dunning basis sets were used, and the convergence test was performed up to aug-cc-pV5Z. Among the computationally feasible methods, ωB97XD performed the best for these non-covalent systems. NBO analysis was performed to investigate the nature of the Rg/AR interactions. In this type of weak interaction, the induced and instantaneous dipole and charge transfer character both contribute to the interaction energies and equilibrium distances.

THEORETICAL CALCULATION OF BOND DISSOCIATION ENERGIES AND HEATS OF FORMATION FOR ALKYL NITRATE AND NITRITE COMPOUNDS WITH DENSITY FUNCTIONAL THEORY AND COMPLETE BASIS SET METHOD

2007 ◽  
Vol 06 (03) ◽  
pp. 449-458 ◽  
Author(s):  
XIAO-HONG LI ◽  
RUI-ZHOU ZHANG ◽  
XIN-LU CHENG ◽  
XIANG-DONG YANG
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Heats Of Formation ◽  
Basis Sets ◽  
Bond Dissociation Energies ◽  
Functional Theory ◽  
Dissociation Energies ◽  
Alkyl Nitrate ◽  
Nitrate And Nitrite

The N – O bond dissociation energies (BDEs) and the heats of formation (HOFs) of alkyl nitrate and nitrite compounds in gas phase at 298.15 K were theoretically calculated. Density functional theory (B3LYP and PBE1PBE) with 6-311+g** and 6-311g** basis sets was employed. It is found that PBE1PBE functional has an average increased BDE of 4.03 kcal/mol from B3LYP functional. What is more, we find the reverse trend in ab initio approach, which is slightly smaller than PBE1PBE. The B3LYP functional is found to be sufficiently reliable to compute the BDEs of alkyl nitrate compounds without the presence of diffusion functions. The BDEs of alkyl nitrite compounds appear to be a constant. The functionals (B3LYP and PBE1PBE) with 6-311g** and 6-311+g** basis sets and CBS-4M ab initio method can all yield good results with respect to the experimental HOFs with the deviation less than 2.0 kcal/mol. As the number of methylene group increases, the HOFs of alkyl nitrate and nitrite compounds increase. In addition, the conclusion of Ventural et al. (J Phys Chem A105:9912, 2001 and Phys Lett245:488, 1995) is confirmed again by our computational results.

scholarly journals Harnessing the Power of Multi-GPU Acceleration into the Quantum Interaction Computational Kernel Program

2021 ◽  
Author(s):  
Madushanka Manathunga ◽  
Chi Jin ◽  
Vinicius Cruzeiro ◽  
Yipu Miao ◽  
Dawei Mu ◽  
...  
Keyword(s):  
Load Balancing ◽  
Ab Initio ◽  
Density Functional ◽  
Large Scale ◽  
Functional Theory ◽  
Multiple Gpus ◽  
Hartree Fock ◽  
Large Size ◽  
Electron Repulsion Integrals ◽  
Computational Kernel

<div><div><div><p>We report a new multi-GPU capable ab initio Hartree-Fock/density functional theory implementation integrated into the open source QUantum Interaction Computational Kernel (QUICK) program. Details on the load balancing algorithms for electron repulsion integrals and exchange correlation quadrature across multiple GPUs are described. Benchmarking studies carried out on up to 4 GPU nodes, each containing 4 NVIDIA V100-SMX2 type GPUs demonstrate that our implementation is capable of achiev- ing excellent load balancing and high parallel efficiency. For representative medium to large size protein/organic molecular sys- tems, the observed efficiencies remained above 86%. The accelerations on NVIDIA A100, P100 and K80 platforms also have real- ized parallel efficiencies higher than 74%, paving the way for large-scale ab initio electronic structure calculations.</p></div></div></div>

Dative versus electron-sharing bonding in N-oxides and phosphane oxides R3EO and relative energies of the R2EOR isomers (E = N, P; R = H, F, Cl, Me, Ph). A theoretical study

2018 ◽  
Vol 20 (17) ◽  
pp. 11856-11866 ◽  
Author(s):  
Tao Yang ◽  
Diego M. Andrada ◽  
Gernot Frenking
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Quantum Chemical Calculations ◽  
Quantum Chemical ◽  
Density Functional ◽  
Theoretical Study ◽  
Basis Sets ◽  
Functional Theory

Quantum chemical calculations using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory using BP86 and M06-2X functionals in conjunction with def2-TZVPP basis sets have been carried out on the title molecules.

Συστηματική κατασκευή βάσεων ατομικών τροχιακών για τον κβαντοχημικό υπολογισμό ηλεκτρικών ιδιοτήτων μορίων

2012 ◽  
Author(s):  
Κωνσταντίνος Μακρής
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Basis Sets ◽  
Functional Theory ◽  
One Dimensional ◽  
Gaussian Type ◽  
One Dimensional Nanostructures

Σκοπός της παρούσης διδακτορικής διατριβής είναι ο σχεδιασμός, με ταυτόχρονη βελτιστοποίηση ενός ή και δύο ταυτόχρονα εκθετών συναρτήσεων πόλωσης, γκαουσιανών (Gaussian type functions, GTF) συνόλων βάσεων ατομικών τροχιακών (basis sets) μικρού και πολύ μεγάλου μεγέθους για τα διαλογόνα ΧΥ (X = F, Cl, Br, I και Υ = F, Cl, Br, I). Βελτιωμένες βάσεις ατομικών τροχιακών χρησιμοποιήθηκαν περαιτέρω για τον υπολογισμό των ηλεκτρικών πολυπολικών ροπών (διπολική έως δεκαεξαπολική) καθώς και των (υπερ)πολωσιμοτήτων των διαλογόνων XY. Μελετήθηκε επίσης επίδραση του μήκους του δεσμού για όλες τις ανωτέρω ιδιότητες με τη χρήση μεθόδων ab initio και Density Functional Theory (DFT). Οι βάσεις χρησιμοποιήθηκαν επίσης στον ab initio υπολογισμό των ηλεκτρικών ιδιοτήτων προτύπων μονοδιάστατων αλυσίδων-νανοδομών (one-dimensional nanostructures, 1D nanowires) της μορφής FY (Υ= F, Cl, Br, I). Μελετήθηκε η εξέλιξη των ηλεκτρικών ιδιοτήτων τους ως συνάρτηση του αριθμού των δομικών μονάδων.

On the Electric Dipole (hyper)polarizability of Difluorodiacetylene (F-C≡C-C≡C-F)

2006 ◽  
Vol 2 (1-2) ◽  
pp. 15-19 ◽  
Author(s):  
G. Maroulis
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Molecular Properties ◽  
Basis Sets ◽  
Dipole Polarizability ◽  
Functional Theory ◽  
Consistent Field ◽  
B3lyp Method ◽  
Self Consistent ◽  
Self Consistent Field

We report static dipole polarizability and hyperpolarizability values difluoroacetylene obtained from finite-field density functional theory and conventional ab initiocalculations with especially designed flexible basis sets of Gaussian-type functions. Our results show that electron correlation has a small effect on the dipole polarizability but a strong one on the hyperpolarizability. The widely used B3LYP method yields molecular properties fairly close to the ab initio ones. The effect of the fluorination on the molecular properties is quite obvious at the self-consistent field level of theory: ᾱ (FCCCCF) < ᾱ (HCCCCF) < ᾱ (HCCCCH) and γ̄ (FCCCCF) < γ̄ (HCCCCF) < γ̄ (HCCCCH).

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